matroskadec: fix potential mem leak

may or may not fix CID134 and CID135


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@13636 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavformat/matroskadec.c

@@ -505,6 +505,7 @@ ebml_read_ascii (MatroskaDemuxContext *matroska,
         offset_t pos = url_ftell(pb);
         av_log(matroska->ctx, AV_LOG_ERROR,
                "Read error at pos. %"PRIu64" (0x%"PRIx64")\n", pos, pos);
+        av_free(*str);
         return AVERROR(EIO);
     }
     (*str)[size] = '\0';